Bioremediation refers to the conversion of toxic environment contaminating compounds into innocuous substances by way of microbial digestion. Bioremediation has been successfully used to treat contaminated soil in above-ground treatment systems, above-ground slurry bioreactors, slurry pits, above-ground soil heaps, composting material, and in situ. A good example of in situ soil treatment came following the Exxon Valdez oil spill in Prince William Sound, Alaska. This oil contaminated miles of Alaskan shoreline and an approximately 70 mile section of shoreline was treated using bioremediation. This remediation process as it was employed focused on enhancing the indigenous microorganisms' growth and oil degrading activities through the application of nutrients.
Representative disclosures of bioremediation process include U.S. Pat. No. 4,035,289, to Michel Guillerme et al., which discloses a method for removing hydrocarbon residues from the effluents from oil well drilling. This method involves culturing microorganisms in a portion of the effluent and then adding the portion back to the remainder to degrade the hydrocarbons. Genetic Engineering News, vol. 9, No. 10 (Nov.-Dec. 1989) at page 3 presents a good example of the in situ bioremediation processes used to assist the clean-up of the Exxon Valdez oil spill in Prince William Sound, Alaska.
It is known that speeding the bioremediation process, by promoting the growth and activity of the waste-degrading microorganisms is desirable. In most situations the microorganisms naturally present in the soil and groundwater are capable of degrading the contaminating compounds. For a successful remediation, the bioremediator must enhance the growth and activity of these naturally occurring microorganisms. To that end, it is understood that supplying the microorganisms with nutrients and advantageous environmental conditions is beneficial. Just noted U.S. Pat. No. 4,035,289 teaches the addition of nitrogen and phosphorus sources to its culturing medium. U.S. Pat. No. 4,727,031 to Richard A. Brown et al., describes a composition of nutrients and a method of using the composition to stimulate the growth of aerobic bacteria, and particularly bacteria capable of hazardous waste degradation. This patent makes reference to Busch, Aerobic Biological Treatment of Waste Waters, Oligodynamics Press, Houston (1971), at page 107, for teaching that phosphorus and nitrogen are critical growth-limiting nutrients and when not present must be added to aerobic bacteria, such as those found naturally occurring in soil and water environments. Other similar disclosures of bioremediation include U.S. Pat. No. 3,846,290 to Richard Raymond, which discloses the advantageous injection of nutrients into subsurface water supplies to reduce contaminating hydrocarbons; U.S. Pat. No. 4,401,569 to Vidyut Jhaveri et al., which similarly shows injecting nutrients into the ground to enhance microbial action on contaminants; U.S. Pat. No. 4,925,802 to Michael Nelson et al., which shows adding an amino acid to bioremediation systems; U.S. Pat. No. 4,849,360 to Edward Azarowicz, which shows a multitank digestion process for degrading oily wastes; and U.S. Pat. No. 4,493,895 to Joseph F. Colaruotolo et al., which shows particular microorganisms which are capable of dissimilating halogenated compounds into the natural carbon cycle.
In general, therefore, bioremediations are speeded by adding nutrients, pH adjusters, and if aerobic microorganisms are used, oxygen to the soil and/or water of interest. By adjusting these parameters the indigenous microorganisms will multiply and become more active resulting in faster waste degradation. It only becomes necessary to add "foreign" microorganisms to the contaminated environment if the indigenous microorganisms do not posses the genes needed to create the enzymes necessary to degrade the contaminant, if the contaminant is at such a high concentration as to be toxic to the natural microorganisms, or if the contaminant concentration is so low the natural level of microorganisms cannot further degrade it to an acceptable level.
In most cases, bioremediations are performed in environments such as on site locations which can be classified as open systems. In the case of biodegradation in a closed environment, such as a batch bioreactor, it is sufficient to use an aqueous culture medium which completely and immediately supplies the microorganisms with the various nutrients required to increase degradation rates. These various nutrient elements are discussed in U.S. Pat. Nos. 4,035,289 and 4,727,031 which were noted above. Nutrient needs in open systems cannot be efficiently filled using the teachings of U.S. Pat. No. 4,035,289. This is because this patent shows the application of nutrient compounds which have virtually no ability to remain in the microorganisms' environment for extended periods in an open system. In this situation, it is necessary to apply these nutrients repeatedly to the open system throughout the remediation's duration.
The resulting depletion-reapplication cycle puts the microorganisms in a stressed state, and the microbes degradative efficiency is reduced. In addition, the washing away of the nutrients, from the point of application, is wasteful and may actually add to the environmental problem. One example of a nutrient runoff problem is blue baby syndrome which is caused by nitrates contaminating "potable" water supplies. This nutrient loss may be avoided to some extent by supplying nutrients in a form which can be associated or bound with the contaminant, such as a hydrocarbon waste, to provide a localized growth medium for the microorganisms.
U.S. Pat. No. 3,943,066, to Pierre Fusey, discloses a method for nutrient-waste mass association using an aqueous biodegradable emulsion of nitrogen- and phosphorus-containing substances with the hydrocarbon waste. In U.S. Pat. No. 4,460,692, to Jacques Tellier et al., a lipophilic microemulsion of an aqueous nutrient solution is applied in a layer upon the waste mass. These methods provide a way to associate essential nutrients onto the surface of the organic waste, but do not provide a controlled rate of nutrient release to the microorganisms' environment. In another, related disclosure, U.S. Pat. No. 4,401,762, also to Jacques Tellier et al., describes a process of culturing microorganisms using a microemulsion of nutrients and the use of this process in biodegradation settings.
The present invention addresses the problem of nutrient delivery to bioremediation environments by using controlled-release nutrient delivery systems engineered specifically for microorganisms. Controlled-release compositions have been used heretofore to provide nutrients to growing organisms, such as plants. See, for example, U.S. Pat. No. 4,657,576 to Johannes Lambie, which discloses a fertilizer composition for releasing nutrients to plants throughout the growing season; U.S. Pat. Nos. 3,300,293 and 3,252,786 to Andrew Bozzelli et al., which each relate to a slow-release fertilizer composition comprising a dispersion of urea-wax adduct in wax and its use fertilizing crops; U.S. Pat. No. 3,259,482 to Louis Hansen, which describes a slow-release fertilizer having a plurality of epoxy-polyester resin coatings and its use with plants; U.S. Pat. No. 3,232,739 to Steven Belak, which describes a polyurethane foam extended with free urea and the ability of the foams to supply urea fertilization to a plant throughout a long period of time; U.S. Pat. No. 3,252,786 to Andrew Bozzelli et al., which involves slow-release fertilizer compositions containing urea, wax, rosin, and optionally asphalt, and their use in fertilization processes; U.S. Pat. No. 3,475,154 to Haruhiro Kato et al., which describes resin-coated fertilizer particles and their use in garden settings; U.S. Pat. No. 4,120,685 to Silvio Vargiu et al., which describes fertilizers capable of achieving slow-release of nitrogen from urea-formaldehyde mixtures; U.S. Pat. No. 4,563,208 to Peter Backlund, which shows that fertilizer particles can be covered with a reaction product of urea and metal oxides; U.S. Pat. No. 4,210,437 to Robert Windgassen et al., which shows liquid fertilizer compositions which provide sulfur, nitrogen and micronutrient metals; and U.S. Pat. No. 4,756,738 to William J. Detroit, which shows a copolymer matrix which is capable of gradually releasing fertilizer.
Additional patents of note are U.S. Pat. No. 4,111,201, to Felix Theeuwes, and U.S. Pat. No. 3,952,741, to Richard Baker, which discloses devices capable of osmotically delivering beneficial agents. While for the most part, these patents are directed to delivering pharmaceutical agents to patients, they do generally include the delivery of any "active agent", including in the case of U.S. Pat. No. 4,111,201 microorganism attenuators, fermentation agents, nutrients and other agents that "benefit the environment of use" and in the case of U.S. Pat. No. 3,952,741, any agent in any way affecting any biological entity.
The current invention improves the efficiency of bioremediations in soil and/or aqueous environments by providing controlled-release compositions which supply nutrients to the microorganisms in a regulated, environmentally sound, and cost effective manner.